With any substance you are thinking of trying the main issue is allergic reaction, you may find something will cause a really nasty reaction so best to test first. Now inside your cunt is somewhat more sensitive than outside but for the purpose of the test your upper inside thigh is sensitive enough to test on. So before you go heaping something unknown into your fuck hole try spreading some around on the skin of your inside thigh. The sensation you want is something you can feel, it will be more intense inside of course, the thing to look out for is any lasting redness or swelling. If after 20-30 minutes there is significant redness or lumpy swelling DO NOT use this stuff inside. If everything looks ok then you can proceed, still use caution and start off with a little then you can increase the amount.
Ok caution and warning out of the way I can tell you I have used a lot of really odd shit inside cunts with no lasting effects. The list will vary from person to person so always test first.
Heat balms, things like Vicks, Bengay, Deepheat, Icyhot, and even Tiger Balm. I have one sub friend so obsessed with Tiger Balm she uses it just about any time she masturbates, but be warned it is STRONG.
Bathroom products, perfume, aftershave, toothpaste, shaving cream and hair mousse.
Kitchen, fresh peeled ginger, mustards, some chilli sauces but be careful with these especially Tabasco as that does react badly on a lot of people.
And one final step, thoroughly wash out any remains with warm water and use a mild vinegar douche (2 tablespoons white vinegar per litre of water) to help restore ph balance.